Removable and/or replaceable humidifier

ABSTRACT

Humidifier apparatus for a respiratory apparatus includes a housing providing a gas flow path, a heater apparatus, and a water supply distribution member configured and arranged to deliver water vapor to the gas flow path. The water distribution member is provided to the housing and in thermal communication with the heater apparatus.

CROSS-REFERENCE TO APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/213,958, filed Jun. 26, 2008, which claims priority to AustralianApplication No. AU 2007903508, filed Jun. 28, 2007, the entire contentsof each which is incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to humidification arrangements used tocontrol the humidity of breathable gases used in respiratory apparatusventilation systems including invasive and non-invasive ventilation,Continuous Positive Airway Pressure (CPAP), Bi-level therapy andtreatment for sleep disordered breathing (SDB) conditions such asObstructive Sleep Apnea (OSA), and for various other respiratorydisorders and diseases.

2. Description of the Art

Respiratory apparatus commonly have devices to alter the humidity of thebreathable gas in order to reduce drying of the patient's airway andconsequent patient discomfort and associated complications. The use of ahumidifier placed between the positive airway pressure device (or flowgenerator) and the patient mask produces humidified gas that minimizesdrying of the nasal mucosa and increases patient airway comfort.

Many humidifier types have been proposed, including humidifiers that areeither integrated with or configured to be coupled to the relevantrespiratory apparatus. While passive humidifiers can provide somerelief, generally a heated humidifier is required to provide sufficienthumidity and temperature to the air so that patient will be comfortable.

Humidifiers typically comprise a water tub having a capacity of severalhundred milliliters, a heating element for heating the water in the tub,a control to enable the level of humidification to be varied, a gasinlet to receive gas from the positive airway pressure device, and a gasoutlet adapted to be connected to a gas conduit that delivers thehumidified pressurized gas to the patient's mask.

Tub-of-water humidifiers are vulnerable to liquid water spillage if theyare not maintained in a substantially vertical orientation. Spillage ofliquid water can either travel into the gas conduit to the patient orback into the positive airway pressure device and associated electronicsor deplete the reservoir of humidifying water. In either of the cases,the spillage of water is undesirable.

A semi-permeable membrane may be used to isolate the liquid water fromthe gas flow. The semi-permeable membrane has the characteristic ofallowing water vapour to pass through it but not liquid water. Watervapour passing through the semi-permeable membrane may be entrained intothe gas flow within the humidifier and then passed to the patient.

U.S. Pat. Nos. 3,871,373, 4,146,597 and 4,155,961 disclose the use oftubes of semi-permeable membrane, containing liquid water, inserted intothe gas flow path. The tubes are used as a source of water vapour forentraining into the passing gas flow stream.

U.S. Pat. Nos. 4,753,758 and 4,921,642 disclose the use of asemi-permeable membrane to separate a water chamber and a gas flow pathchamber of a humidifier. In these examples, the water and gas flowchambers are typically generous in their volumes with consequently ahigh thermal capacity and slow thermal response.

U.S. Pat. Nos. 4,910,384 and 5,062,145 disclose a heater situated withina water-containing envelope of semi-permeable membrane material,dividing the gas chamber in two.

In U.S. Pat. No. 4,657,713, a heater block of the humidifierincorporates a water supply and a semi-permeable filter membrane.

None of these prior art devices provide a satisfactory solution to theprovision of humidified breathable gas to the patient, nor to the easeof construction, disposability, retrofitting and hygiene requirementsfor a humidification device.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a humidifier apparatuswhich overcomes or ameliorates disadvantages of the prior art.

In one embodiment, a humidifier apparatus comprises a housing whichincludes a gas inlet and outlet for the gas flow, a water supplydistribution member that supplies water vapour to the gas flow and aheater apparatus that is in thermal contact with the water supplydistribution member. The water supply distribution member hasadaptations so that it is a removable and replaceable fitting to thehumidifier apparatus.

In an embodiment, at least a part of the heater apparatus is also aremovable and replaceable fitting to the humidifier apparatus.

In a further embodiment, aspects of the humidifier apparatus may bedisposable or the humidifier apparatus may provide one or moresub-components which may be removable for either replacement or re-useafter servicing. For example, a thin, envelope form of the water supplydistribution member may be disposable.

A further aspect of the invention provides that part of the heaterapparatus forms part of the water distribution member. In an embodiment,this part of the heater apparatus may be an induction receiving element.

In an embodiment, the water supply distribution member may include awick and/or capillary action device which provides water forvaporization into the gas flow.

A further aspect of the invention relates to a humidity control devicewhich enables the amount of water vapour passing from the waterdistribution member to the gas flow to be controlled.

In an embodiment, the water supply distribution member may include awater filter.

In an embodiment, the gas flow path, the water distribution member andat least a part of the heater apparatus are located in the humidifierapparatus as a number of thin, adjacent layers. The thin layering ofeach of these components serves to improve the vaporization of the waterand its mixing into the gas flow.

Another aspect of the invention relates to a humidifier apparatus for arespiratory apparatus including a housing providing a gas flow path, aheater apparatus, and a water supply distribution member configured andarranged to deliver water vapour to the gas flow path. The waterdistribution member is provided to the housing and in thermalcommunication with the heater apparatus.

Another aspect of the invention relates to a humidifier apparatus for arespiratory apparatus including a housing, one or more water supplydistribution members removably fitted to the housing, and a heaterapparatus in thermal communication with at least one of the waterdistribution members. The one or more water supply distribution membersare configured and arranged to deliver water vapour to one or more gasflow paths defined by the one or more water supply distribution membersand the housing.

Another aspect of the invention relates to a water distribution memberfor a humidifier apparatus including an envelope formed by a firstcompartment wall and a second compartment wall joined together, and awater inlet into the envelope.

Another aspect of the invention relates to a humidifier apparatusincluding a base plate removably and replaceably attachable to ahumidifier housing, a heater apparatus provided to the base plate, and awater distribution member provided to the base plate. The waterdistribution member includes first and second compartment walls thatdefine an envelope adapted to receive a supply of water. The firstcompartment wall includes a semi-permeable membrane adapted to allowwater vapour to pass therethrough and the second compartment wallincludes a thermally conductive wall in thermal communication with theheater apparatus.

Other aspects, features, and advantages of this invention will becomeapparent from the following detailed description when taken inconjunction with the accompanying drawings, which are a part of thisdisclosure and which illustrate, by way of example, principles of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIG. 1 is a schematic perspective view of a humidifier apparatusaccording to an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is an enlarged view of the circled region 4 in FIG. 3;

FIG. 5 is an exploded view of FIG. 3;

FIG. 6 is a schematic perspective view of a water distribution memberaccording to an embodiment of the present invention;

FIG. 7 is an exploded view of FIG. 6;

FIG. 8 is a cross-sectional view across the line 8-8 of FIG. 6 of analternate embodiment of a composite filter structure;

FIG. 9 is a schematic perspective view of a chassis for the waterdistribution member of FIG. 6 according to an embodiment of the presentinvention;

FIG. 10 is a cross-sectional view along the line 10-10 of FIG. 9;

FIG. 11 is an alternate embodiment of the humidifier apparatus in FIG.2, where devices for humidity control are introduced according to anembodiment of the present invention;

FIG. 12 is an enlarged view of the circled region 12 in FIG. 11;

FIG. 13 is an alternate embodiment, to that in FIG. 12, for humiditycontrol;

FIG. 14 schematically illustrates the partial shutter position for thehumidity control embodiment of FIG. 13;

FIG. 15 schematically illustrates the no humidification shutter positionfor the humidity control embodiment of FIG. 13;

FIG. 16 is a cross-sectional view of a humidifier apparatus includinganother alternate embodiment for humidity control;

FIG. 17 is a cross-sectional view of a humidifier apparatus includingyet another alternate embodiment for humidity control;

FIG. 18 is a partial, cross-sectional view of a further embodiment ofFIG. 3 where an external water reservoir is introduced; and

FIG. 19 is a different, partial cross-sectional view of the embodimentof FIG. 18.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The following description is provided in relation to several embodimentswhich may share common characteristics and features. It is to beunderstood that one or more features of any one embodiment may becombinable with one or more features of the other embodiments. Inaddition, any single feature or combination of features in any of theembodiments may constitute additional embodiments.

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise”, “comprised” and “comprises” where they appear.

The term “air” will be taken to include breathable gases, for exampleair with supplemental oxygen.

FIGS. 1 to 5 schematically show a first embodiment of a humidifierapparatus 110 for delivering water vapour into a breathable gas flowproduced by a positive airway pressure device (or flow generator) of arespiratory apparatus such as a Continuous Positive Airway Pressure(CPAP) therapy machine.

With reference to FIG. 1, the humidifier has a housing 112 which definesan upper internal gas flow path, described below with reference to FIG.2. The housing 112 includes a gas inlet 114, which receives gas flow(indicated by an arrow) from the positive airway pressure device (notshown), a low-profile centre section 116 and gas outlet 118.

In use, the gas outlet 118 of humidified breathable gas flow (indicatedby an arrow) is typically connected to a patient conduit (not shown)which in turn is connected to the patient's mask. The form of theconnectors for the gas inlet 114 and the gas outlet 118 may be of anysuitable, conventional connector to enable connection to the positiveairway pressure device and the patient conduit. The housing 112 also mayhave a water inlet passage 120 adapted for connection to a supply ofliquid water for the humidifier apparatus. The water supplied is usedfor the humidification of the gas passing through the humidifierapparatus 110.

The housing 112 of the humidifier apparatus 110, as shown in FIG. 1, maybe of a material that is light, durable to heat and water and approvedas safe for use in respiratory medical apparatus. In addition, thematerial may be sufficiently resilient to allow easy connection of theappropriate fittings to the gas inlet 114 and the gas outlet 118.Preferable materials for the housing are resilient plastic likematerials, for example polycarbonate, polycarbonate ABS blends orpolypropylene. However, the housing may be constructed of other suitablematerials.

In one embodiment, the housing 112 as shown in FIG. 1 may be generallyrectangular in plan view with example dimensions of: approximate length122 of 120 to 150 mm and a breadth 124 of 100 to 120 mm. The housing 112may also have a downwardly extending peripheral flange 126 approximately5 to 20 mm in height. The dimensions and shape of the housing 112 givenhere and later are given by way as examples for the embodimentsdescribed here. Other dimensions and shapes to those given may also beused, for example depending on the humidification capacity of thehumidifier apparatus 110 and/or for compatibility with respiratoryapparatus.

FIG. 2 is a cut away view taken along line 2-2 in FIG. 1, showing theinternal components and gas flow path 210 (indicated by the arrows),within the humidifier apparatus 110.

The gas flow path 210 flows through the low profile centre section 116of the housing 112 and over a water distribution member 211 that has afirst compartment wall 212 which separates a liquid water layer 214 fromthe gas flow path 210. The low profile centre section 116 of the housing112 and the first compartment wall 212 form a gas passage layer 213between the gas inlet 114 and gas outlet 118. The gas flow 210 receiveswater vapour 216 through the first compartment wall 212 into the gaspassage layer 213, as indicated by arrows, so that ambient gas 210Aentering the humidifier apparatus 110 is humidified in the low profilecentre section 116 and exits as humidified gas 210B.

A second compartment wall 218, which is also part of the waterdistribution member 211, separates the water layer 214 from a heaterapparatus 220. The heater apparatus 220 is used to heat the water layer214 to aid in the generation of water vapour 216 for the gas flow 210(e.g., heater heats water layer to at least 100° C. to produce watervapour). A detailed description of the heater apparatus 220 is givenbelow.

The function of the water distribution member 211 (including the firstcompartment wall 212, the water layer 214, and the second compartmentwall 218) is to distribute water to the gas passage layer 213.

The humidifier apparatus 110 has a base plate 222 which fits into thehousing 112, by being received within a downwardly extending peripheralflange 126 of the housing 112. When the base plate 222 is fully insertedinto the base of the housing 112, the base plate 222 abuts against theperiphery of the second compartment wall 218 and against a shoulder 224of the housing 112. In this position, the base plate 222 providessupport to the water layer 214 via the second compartment wall 218 andprovides a gas seal to the gas flow path 210. The base plate 222 alsoprovides support to the heater apparatus 220. A flexible ridge 226 whichis part of or joins the flange 126 aids in securing the base plate 222against the shoulder 224 of the housing 112. In alternative embodiments,the securing function of the ridge 226 may replaced by conventionalsecuring rings, pins, screws or other fastening devices for securing ascommonly used by those skilled in the art.

The gas passage layer 213 may have by way of example breadth and lengthdimensions of about 50 to 150 mm respectively, e.g., about 100 by 100mm. The thickness of the gas passage layer 213 above the firstcompartment wall 212 may be in the range of about 2 to 20 mm, e.g.,about 5 to 15 mm (e.g., about 10 mm). The housing 112 with the firstcompartment wall 212 defines a gas volume in the humidifier apparatus110 of about 50 to 500 ml, e.g., about 50 to 250 ml (e.g., about 80-150ml). As described above, the dimensions and capacities given here andlater are given by way as examples for the embodiments described. Otherdimensions and capacities to those given may be used.

FIG. 3 is a cut away view taken along line 3-3 in FIG. 1. FIG. 3 showsfurther internal components within the humidifier apparatus 110 and inparticular the water distribution member 211.

FIG. 4 is an enlarged view of the circled region 4 in FIG. 3. Asillustrated, liquid water to replenish the water layer 214 passes intothe humidifier apparatus 110 via the water inlet passage 120 whichincreases in its transverse cross-section in order to distribute wateracross a filter 310 within the water distribution member 211. In anembodiment, the lower section of the water inlet passage 120 is conical.The water inlet passage 120 volume above the filter 310 may also serveas a small reservoir of water for the water layer 214. The filter 310performs as a sterile filter to produce sterile water that may draininto the water layer 214 via a water inlet 312 that is within the waterdistribution member 211. A filter to produce sterile water by removingbacterial and viral disease causing agents may also remove other agents,such as algae and fungal spores, which may lead to the growth ofundesirable agents in the warm and moist environment within thehumidifier apparatus 110. In an alternate embodiment, the filter mayremove particulates and/or dissolved ions from the liquid water toprevent fouling and blockages of the humidifier apparatus 110 in use. Ina further embodiment, the filter 310 may be in the form of a plug whichalso occupies the conical space of the water inlet passage 120 that isabove the first embodiment of the filter 310. In another alternateembodiment, the filter 310 may be omitted from the water distributionmember 211 and the water inlet passage 120 so that the water travelsdirectly from the water inlet passage 120 to the water inlet 312.

Further embodiments of the water distribution member 211 are describedbelow with reference to FIGS. 6 to 9.

Housing Embodiments

In FIGS. 1 and 2, the gas inlet 114 and gas outlet 118 are located ateither end of the length dimension 122 of the humidifier apparatus 110.As illustrated, the gas inlet 114 is shown in a horizontal orientationand the gas outlet 118 is shown in a vertical orientation. However, thelocation and orientation of the gas inlet 114 and gas outlet 118 may bevaried about the humidifier apparatus 110. For example, in an alternateembodiment the gas inlet and outlet 114, 118 may be attached at eitherend of the breadth dimension 124 of the humidifier apparatus 110. Or, inanother embodiment, the gas inlet and outlet 114, 118 may be attachedopposite each other with respect to the length dimension 122 or breadthdimension 124 but with a similar orientation to the horizontal/vertical.In an embodiment, the positioning of the gas inlet and outlets 114, 118is such that they may be opposed to each other across the gas passagelayer 213 in order to maximise the amount of water vapour 216 taken upby the gas flow 210 across the water distribution member 211. As analternative, the gas inlet and outlets may be adjacent to one anotherwith the gas passage layer extending along a tortuous path or a smallerpath sufficient for humidification. Thus, any position for the gas inletand outlets 114, 118 serving this principle may be appropriate.

In yet another embodiment of the housing 112, the generally rectangularplan view shape of the housing may be of any suitable shape. Forexample, the plan view shape of the housing may be circular orelliptical.

In the corresponding embodiments to the housing 112, the gas passagelayer 213, with respect to FIGS. 2 to 5, may be any suitable dimensionsor shape to suit the housing 112 embodiments as described above.Similarly, the water distribution member 211 embodiments, with respectto FIGS. 2 to 10, may have dimensions and shapes to suit the housing 112embodiments as described above.

Removable and Replaceable Fittings

FIG. 5 is an exploded version of FIG. 3. FIG. 5 schematicallyillustrates the various components of the humidifier apparatus 110 whichcan be readily disassembled and re-assembled. The base plate 222 may beseparated entirely and then readily re-attached to the housing 112. Thebase plate 222 is released from the housing 112 by bending back theflexible flange 126 so that the protruding edge of the ridge 226 nolonger secures the periphery of the base plate 222 to the shoulder 224.The base plate 222 may then be re-installed into the base of the housing112 by a simple press fit to negotiate the base plate's 222 peripheraledge past the flexible ridge 226.

When the base plate 222 is removed from the base of the housing 112, theheater apparatus 220 which is seated in the base plate 222 may beremoved and replaced or serviced. In addition, the water distributionmember 211 may be removed from the housing 112 and replaced as adisposable item or serviced and replaced as described below.

In another embodiment, the heater apparatus 220 and base plate 222 arenot separable from each other and form a single component.

When the components described above are removed from the housing 112,the internal surfaces of the housing 112 may be readily accessed forinspection, cleaning or replacing as a disposable item. The waterdistribution member 211 may also be inspected, cleaned and sterilised orreplaced as a low cost disposable item. The heater apparatus 220 andbase plate 222 may be more durable and higher cost components which maybe designed to be re-useable many times, although alternate embodimentsare described below for the heater apparatus 220 and base plate 222 thatare low cost and disposable.

The ability of the humidifier apparatus to be readily disassembled andre-assembled with replaceable components as described above is of aparticular advantage for the on-going ease of maintenance of thehumidifier apparatus 110 by a patient or their carer during the use ofthe respiratory apparatus.

The humidifier apparatus 110 may be readily used by different patientsby attention to the components that are liable to contamination in use.For example, the housing 112 and the water distribution member 211 maybe readily cleaned and sterilised or simply replaced as disposableitems. The base plate 222 and heater apparatus 220 may not becontaminated because they are generally not in contact with the patientor the patient's airway with its associated secretions. Consequently,the base plate 222 and heater apparatus 220 may be re-used.

Water Distribution Member Embodiments

FIG. 6 is a perspective view of the water distribution member 211. Theplane surface of the first compartment wall 212 is shown uppermost withit extending to the shoulder 224 of the housing 112. The firstcompartment wall by way of example may have breadth and lengthdimensions of about 50 to 150 mm respectively, e.g., about 100 by 100mm. The overall dimensions and shape of the water distribution member211 may correspond to that of the gas passage layer 213 and the housing112 embodiments described above.

The first compartment wall 212 is preferably a semi-permeable membranewith the characteristic of preferentially allowing water vapour 216 topass through it but impeding liquid water so that the gas passage layerreceives water vapour 216 but no liquid water from the water layer 214.

The semi-permeable membrane may be formed of a material which has finepores or perforations and may also be hydrophobic, the fineness of theporosity or the perforations and/or the degree of hydrophobicity beingadapted to result in the desired effect of semi-permeability for thisapplication.

Some examples of semi-permeable membrane materials with suitablecharacteristics for use in the water distribution member according to anembodiment of the present invention include:

-   -   Porous polytetrafluroethylene (PTFE) materials, microporous PTFE        membranes and expanded PTFE (ePTFE) from Gore-Tex®, W.L. Gore &        Associates, Inc of Maryland USA.    -   Tyvek® spun polyethylene sheet material from DuPont.    -   PTFE mesh sold as Fluorcarbon SPECTRA/MESH® by Spectrum        Laboratories of Rancho Dominguez, Calif. USA.    -   Fibrous membranes consisting of auxetic fibres (fibres with a        negative Poisson's Ratio).    -   A more comprehensive discussion of suitable semi-permeable        membrane materials is included in Patent Application No. WO        2006/069415 A1 “Respiratory Mask having Gas Washout Vent and Gas        Washout Vent Assembly for Respiratory Mask”, the contents of        which are incorporated herein by reference.

In another embodiment, the surface of the first compartment wall 212 mayhave dimples or corrugations formed within it so as to increase the areaof interaction with the gas flow path 210 and/or to promote theturbulent mixing of the water vapour 216 with the gas flow path 210.

The first compartment wall 212 is joined to the second compartment wall218 by a bonding strip 610 about the periphery of both compartment walls212, 218 to form a thin envelope containing the water layer 214. Thebonding strip 610 between the first and second compartment walls 212,218 may be achieved by heat sealing, an adhesive, welding or anysuitable method of manufacture.

In FIG. 6, the filter 310 is visible thru a filter aperture 612. Thefilter 310 is sandwiched at its periphery by the first and secondcompartment walls 212, 218 which in turn are bounded by the bond strip610. Liquid water flows through the filter aperture 612, the filter 310and into the water layer 214 (not shown in FIG. 6) of the waterdistribution member 211.

The second compartment wall 218 on the underside of the waterdistribution member 211 shown in FIG. 6 may be formed of materials ofthe type and form suitable to conduct heat from the heater apparatus 220into the water layer 214. Desirable properties of the second compartmentwall 218 include that it may be thin so as to conduct and dissipate heatrapidly with very low thermal inertia and structurally robust andflexible so that it may readily conform to the surface of the heaterapparatus 220. Suitable materials for the second compartment wall 218may be metallized plastic film, a metal foil such as aluminium or metalplastic composite. Further embodiments of the second compartment wall218 in combination with the heater apparatus 220 are described belowwith the heater apparatus 220 description.

A thin envelope configuration as described above for the waterdistribution member 211 enables the water layer 214 within to be thin.In an embodiment, the thickness of the liquid water layer 214 by way ofexample may be about 1-5 mm, e.g., less than about 2 mm, however largercapacity versions may have a thickness up to and greater than 10 mm. Thecorresponding volume of the water layer 214, by way of example, mayrange from less than 10 ml to larger capacity versions that may be up toand greater than 150 ml.

A thin water layer 214 of low volume may be heated rapidly with modestheating to produce adequate water vapour 216 for the humidification ofthe gas flow path 210. Modest heating requirements enable a heatingapparatus 220 of low power requirements to be used in the humidifierapparatus 110.

In use, water vapour may also be produced within the envelope of thefirst and second compartment walls 212, 218 as a result of heating fromthe heater apparatus 220. In situations where a high humidification rateis required within the gas flow path 210, the rate of heating by theheater apparatus 220 may be such that considerable amounts of watervapour are present with the liquid water within the water layer 214.

An alternate embodiment of the water distribution member 211 may includethe use of additional, partial bonding strips (not shown) across theplane of the first and second compartment walls 212, 218 that partiallyjoin the compartment walls 212, 218. The additional, partial bondingstrips may be arranged in such a manner to improve the rigidity of thewater distribution member 211, allow water to flow through the waterlayer 214 and to prevent ballooning where the envelope of the first andsecond compartment walls 212, 218 may be inflated by the supply of waterat an excessive pressure or vigorous heating by the heater apparatus 220generating excessive water vapour. Ballooning of the envelope of thefirst and second compartment walls 212, 218 may obstruct the gas passagelayer 213.

Filter Composite Structure

FIG. 7 is an exploded perspective view of the water distribution member211 with an alternative embodiment of the filter 310 to that describedwith reference to FIG. 3 above. In this embodiment, the filter is in theform of a composite filter comprising a filter disc 710 and a filtersupport 712. The filter disc 710 performs the filtering functionsdescribed above for the other embodiments. The filter disc 710 sitsbelow the filter aperture 612 so as to receive all the water from thewater inlet passage 120. The filter disc 710 is supported by and sitswithin the filter support 712 in a manner that allows the water from thewater inlet passage 120 to pass through the thickness of the filter disc710 and freely drain from the lower side of the filter disc 710 to thewater inlet 312. To allow the free draining of the filter disc 710, thefilter support 712 consists of a very porous material which allows thefiltered water to pass freely through it whilst providing structuralsupport to the filter disc 710. The filter support 712 material may beany one of many suitable porous materials such as foam plastics or foamform metals which are approved for medical respiratory apparatus use oralternatively a suitable plate with many through holes or a plate withmany, small, raised protrusions on its surface. To aid in the freedraining function of the filter support 712, ribs 714 are located belowthe filter disc 710. The ribs 714 form rib channels 716 which allow thefiltered water to proceed freely to the water inlet 312 through thefilter support 712 portion adjoining the water inlet 312.

An advantage of the filter composite structure 710, 712, 714, 716described above is that the expensive filtering material is limited to afilter disc 710 to coincide with the filter aperture 612 rather thanoccupying the rest of the filter volume in which the filter support 712resides.

FIG. 8 is a cross-sectional view across the line 8-8 of FIG. 6 of analternate embodiment of a composite filter structure. In thisembodiment, multiple filter walls 810 are used to support a filterinfill 812 where the filter infill 812 performs the filtering functionsdescribed above for the other filter embodiments. The top of the filterinfill 812 corresponds to the filter aperture 612 for receiving thewater for filtering. Along the bottom of each of the multiple filterwalls 810 are a number of filter wall apertures 814 that allow thefiltered water to move from and through a number of bottom channels 816(which are below the filter infill 812) to the water inlet 312 of thewater layer 214. In use, the water flow 818 is indicated by the dashedlines with arrows. For this embodiment, there may be multiple waterinlets 312 depending on the number of filter wall apertures 814 in thefilter wall 810 adjoining the water layer 214.

In an alternative embodiment to those described above, the filter 310,710, 712, 714, 716, 810, 812 may be omitted and/or optional. In thisembodiment, the liquid water may pass freely through the filter aperture612, through the water inlet 312 and into the water layer 214 as boundedby the first and second compartment walls 212, 218.

Chassis for Water Distribution Member

The single structure form of the water distribution member 211facilitates it being readily removable from the humidifier apparatus 110and being replaceable as described above with reference to FIG. 5 andbelow with reference to FIGS. 9 and 10.

FIG. 9 is a perspective view of a chassis 910 that may be used as afurther embodiment for the support of the water distribution member 211according to any one of the water distribution member 211 embodimentsdescribed above. The chassis 910 may be made of a material which isrigid, such as plastic or a metal frame. To improve the rigidity of thechassis 910, braces 912 may be incorporated in the underside of thechassis 910. The braces 912 are shown in dashed outline on FIG. 9 inorder to represent their location under the water distribution member211. The braces 912 are of a thin profile and of an appropriate materialfor contact with the heater apparatus 220.

The chassis 910 may have a protruding tab 914 that facilitates theinsertion and removal of the chassis 910 and water distribution member211 to the humidifier apparatus in the direction shown by thebi-directional arrow 916. The arrangement (not shown) for accommodatingthe chassis 910 into the humidifier apparatus 110 may comprise ofincreasing the downward length of the flange 126 and increasing thedistance between the shoulder 224 of the housing 112 and the peripheryof the base plate 222 in order to allow the chassis to slid in and outof a space between the shoulder 224 and the base plate 222. In order forthe chassis 910 to access this space, the flange 126 along the lengthdimension 122 may be omitted. In addition, the profile of the chassis910 may be adapted so that as it slides into the humidifier apparatus110 the periphery of the water distribution member 211 is caused to makea gas tight seal with the shoulder 224 of the housing 112. Similarly,the second compartment wall 218 of the water distribution member 211 iscaused to be in thermal contact with the heater apparatus 220.

The chassis 910 may be secured in position within the humidifierapparatus 110 by any one of many mechanical options available to aperson skilled in the art.

FIG. 10 is a cross-sectional view along the line 10-10 of FIG. 9. FIG.10 illustrates how the water distribution member 211 is contained withinthe chassis 910. The water distribution member 211 may simply restwithin the chassis 910.

The advantage of an alternate embodiment including a chassis 910 is thata simple single step sliding action to replace the water distributionmember 211 may be done rather than a more involved action of the removalof the base plate 222 and the heater apparatus 220 as described in otherembodiments above.

In another embodiment, the humidifier may have a hinged upper section toallow access to the water distribution member for easy insertion andreplacement.

Wick Embodiment

An alternative embodiment for the water distribution member 211 is theuse of a wick and/or capillary action device (not shown) in place of thefirst compartment wall 212 and the water layer 214. The wick device hasthe ability to conduct water upon or within the wick device such thatwater is available for vaporisation into the gas passage layer 213. Inaddition, a capillary action may also be involved within the wickdevice. An example of a suitable wick device is a material which ishydrophilic so that the water has a tendency to spread across the extentof the material. Materials that may be suitable include cotton,activated perfluorinated polymer (e.g., “NAFION” stabilisedperfluorosulfonic acid/PTFE copolymer by DuPont), polyester copolymer(e.g. SYMPATEX polyester/polyether copolymer by Sympatex TechnologiesGmbH of Germany) and polyester fabrics (e.g., COOLMAX polyester fabricsby Invista of USA). Alternatively, a material may be impartedhydrophilic characteristics by using a particular liquid film or theapplication of a gel or solid film.

The wick device may have an internal structural form of a fabric,sponge, a film, a bundle of fibres or a hydrophilic porous, flexiblesolid, e.g., plastic, metal or ceramic. The external form of the wickdevice may be of a continuous liner upon the second compartment wall218. In an alternate embodiment of the external form, the wick deviceliner may be in the form of a corrugated or dimpled liner upon thesecond compartment wall 218 so that the area of interaction between thegas flow path 210 and the wick device is increased.

Alternatively, the wick device may be in the form of a very gas porousmembrane that may extend partially or wholly across the transverse crosssection of the gas passage layer 213, the material forming the membranebeing as per that described above for the wick.

In another embodiment of the wick device, the second compartment wall218 may be omitted and the wick device as a continuous sheet may bejoined to a peripheral frame in place of the bond strip 610 described inthe above embodiments. In a further embodiment, a grid support structuremay be located with the continuous sheet of the wick device and also bejoined to the peripheral frame.

The water supply for the wick device may be in the forms described abovefor the other embodiments of the water distribution member 211.

In a further hybrid embodiment of the water distribution member 211, thewick device may reside within the envelope formed by the compartmentwalls 212, 218, as described above for the other embodiments.

Heater

For all the above described embodiments of the water distribution member211, a heater apparatus 220 may be used to increase the amount of watervapour 216 produced by the water distribution member 211. The heaterapparatus 220 may consist of a heating element (not shown) embeddedwithin or attached to a metal or ceramic block which is against thesecond compartment wall 218. The heating element may for example consistof a resistive conductor. The conductor may consist of multipleresistive conductors connected to each other in series, parallel orsegmented about the heater apparatus 220 in order to allow uniform,variable and/or sectional heating of the second compartment wall 218 andthrough it the water layer 214.

The base plate 222, as well as providing support as described above,insulates the heater apparatus from any surface that the humidifierapparatus 110 may rest upon. The base plate 222 may be made of amaterial or a composite of materials which provide suitable refractoryproperties for the temperature range of the heater apparatus 220 andsuitable insulation properties. A person skilled in the art ofmanufacture may select from any one of many widely available materialssuitable for the purpose, for example a ceramic composite or a varietyof high temperature plastics.

In addition, the base plate 222 may have electrical connections (notshown) to which the heating element of the heater apparatus 220 mayconnect with in a manner that allows the base plate 222 to be readilydisassembled and re-assembled to the heater apparatus 220 as describedabove with reference to FIG. 5. The external surface of the base plate222 may have corresponding electrical connections (not shown) so thatthe heating element may receive its electrical power supply from therespiratory apparatus that the humidifier apparatus 220 may be connectedwith or alternatively the heating apparatus may have its own powersupply. The form and materials that may be used for the electricalconnections may be any suitable one of the many options available to aperson skilled in the art. For example, the metal electrical contactsmay be of a male-female engagement arrangement or a simple, flat slidingcontact.

In an alternative embodiment, the heater apparatus 220 may be locatedwithin a section of the respiratory apparatus that the humidifierapparatus 110 sits upon. The heater apparatus 220 may have a heaterplate (not shown) which may be in thermal contact with the base plate222 when the humidifier apparatus 110 rests upon the respiratoryapparatus. The base plate 222 in this embodiment is of a suitablythermally conductive material, such as a metal, which is also in thermalcontact with the second compartment wall 218.

In a further embodiment, the base plate 222 and the second compartmentwall 218 may be combined in a single structure to form a heater platethat may be comprised of thin metallised foil in the portion adjacent tothe water layer 214. A peripheral support rim for the heater plate 218,222 may be used to secure the water distribution member 211 against theshoulder 224 with the ridge 226.

Filament or Strip Heater

In another embodiment, the heater apparatus 220 may be in the form of afilament or tape heater element which may be attached to the side of thebase plate 222 which is adjacent to the second compartment wall 218. Inan alternative embodiment, the filament or tape heater element may beattached to or incorporated within the second compartment wall 218. Inyet another embodiment, the filament or tape heater element may belocated within the water layer 214 or in the wick device embodiment ofthe water distribution member 211 the heater element may be interwovenwith or adjacent to the wick device as described above. The necessaryelectrical connections to the electrical power supply are as describedabove.

The filament heater element may be in the form of a conventionalresistive wire heater. The tape heater element may be a flexible tapeheater as described in Australian Patent Application No. 2006906224“Humidifier for a Respiratory Apparatus”, the contents of which areincorporated herein by reference. In one embodiment of the flexible tapeheater, the heating element may be formed by printed circuit techniquesapplied to a surface of a flexible substrate such as silicone rubber,all-polyimide or PTFE. Included in the printed circuit techniques whichmay be used are etched foil, printing and vacuum deposition techniques.The Thermofoil™ range of the type of flexible heaters by Minco ofMinneapolis USA, described at www.minco.com, are examples ofcommercially available strip heaters which may be modified for use inthe present application. Alternatively, the flexible tape heater may beformed as a heating element, for example in the form of a resistive wireor ribbon, laminated between tapes of polycarbonate or other suitableplastics film.

Induction Heater

An alternate embodiment of the heater apparatus 220 may comprise of aninduction heating system. In such a system, a transmitting inductioncoil is used to generate electromagnetic radiation which may betransmitted without the requirement for an electrical, magnetic ormechanical connection to an induction receiving element. Theelectromagnetic radiation induces eddy currents within the inductionreceiving element which may then heat the heater element by electricalresistance heating (Joule effect). In an alternate embodiment, a designof the induction heating system may use magnetic hysteresis losses forheating in the induction receiving element with or instead of eddycurrent resistive heating.

Induction heating systems may be designed and fabricated by a personskilled in the art of induction heating systems as well as by referenceto novel induction heaters such as in Patent Application No.PCT/AU2007/000274 “Induction Heating System and Method for Humidifier”,the contents of which are incorporated herein by reference.

For the humidifier apparatus 110, the transmitting induction coil (notshown) together with the associated power supply and control system maybe located with the respiratory apparatus. The humidifier apparatus 220may be located in the vicinity of the induction coil, sufficiently closethat the induction receiving element (not shown) within the humidifierapparatus 220 receives sufficient electromagnetic radiation from theinduction coil to induce heating. The induction receiving element may belocated between the base plate 222 and the second compartment wall 218such that it is in thermal communication with the second compartmentwall 218. The base plate 222 may be made of materials or of structure towhich induction by electromagnetic radiation does not significantlyoccur. For example, a non-conducting ceramic, plastic or a laminationarrangement of metal and an insulator/dielectric.

In an alternative embodiment, the second compartment wall 218 forms aninduction receiving element. The second compartment wall 218 maycomprise in part at least of a metal foil that is sufficientlyconducting to have eddy currents induced within it and/or sufficientlymagnetisable to undergo magnetic hysteresis under the appliedelectromagnetic radiation. In a further embodiment, the base plate 222may be omitted.

An induction heating system offers the advantage that the inductionreceiving element may have a very low thermal inertia such that it maybe heated to in excess of 100 degrees Celsius within a short time, forexample less than 2 minutes to enable the rapid generation of watervapour 216. Similarly, the low thermal inertia of the inductionreceiving element enables a rapid cooling down, particularly when thewater layer 214 thickness is thin. In addition, for the embodiment wherea low cost induction receiving element is incorporated in the secondcompartment wall 218, the disposability of the water distribution member211 is improved.

Cooling and Heating by the Heater Apparatus

In a further embodiment to the heater apparatus 220 embodimentsdescribed above, the heater apparatus 220 may be a Peltierthermo-electric element that may be used to cool or heat. The Peltierthermo-electric element may be present within the humidifier apparatus110 or external to it as per the embodiments described above. Electricalsupply and control of the Peltier thermo-electric element to heat orcool may be by the respiratory apparatus or a separate electrical supplyand control unit.

The Peltier thermo-electric element may be used to cool the water layer214 to well below the ambient temperature so that the generation ofwater vapour 216 is minimal and consequently there is minimalhumidification of the gas passage layer 213 and the gas flow 210B fromthe humidifier apparatus 110. Conversely, the Peltier thermo-electricelement may be used to variably heat the water layer 214 to produce thedesired amount of water vapour 216 to humidify the gas flow 210B fromthe humidifier apparatus 110.

Sterilisation

In a further embodiment, in-situ high temperature sterilisation may beused with the heater apparatus' 220 capacity to rapidly heat to atemperature in excess of 100 degrees Celsius for a predetermined periodof time. The low thermal inertia of the humidifier apparatus 110 allowsfor its rapid cool down and subsequent use for humidification. Such asterilising technique offers a convenient method to counteract thelodgement and growth of disease causing agents within the humidifierapparatus 110. An alternative sterilisation method may be by the use ofa chemical treatment to one or more surfaces or materials within thehumidifier apparatus 110, for example the water distribution member 211may be permanently impregnated with a chemical that inactivates virusesand arrests bacterial growth.

Humidity Control

FIG. 11 is a further embodiment of that in FIG. 2 where structures areintroduced to enable the amount of humidification of the gas flow path210 to be controlled. The gas passage layer 213 is vertically split by aplate 1110 into two further passage layers, each for a stream of thedivided gas flow path 210A. The humidification gas stream 210C travelsin the lower passage layer 1112 along the first compartment wall 212 andmay receive water vapour 216 being issued from the first compartmentwall 212. The other stream is the dry gas stream 210D which travelsalong the upper passage layer 1114 and is not humidified. The humidifiedand dry gas streams are recombined at the exit end of the upper andlower passage layers 1112 and 1114 to form the humidified gas flow 210Bwhich flows out of the humidifier apparatus 110 via the gas outlet 118.

At either end of the upper passage layer 1114 are a pair of miniatureupper butterfly valves 1116 which can be used to vary the amount of gasflow 210A entering into the upper passage layer 1114. In FIG. 11 theupper butterfly valves are shown in the open position to allow gas flow210A to pass freely through as gas flow 210D. The lower passage layer1112 at either end also has a pair of miniature lower butterfly valves1118, which in FIG. 11 are shown in the closed position.

FIG. 12 is an enlarged view of the dash encircled region 12 in FIG. 11.FIG. 12 illustrates the functioning of the upper and lower butterflyvalves 1116, 1118. In this valve configuration, there is no gas flowthrough lower passage layer 1112 and so no humidification of the gasflow 210 may occur. Only dry gas flow stream 210D may occur. If the pairof lower butterfly valves 1118 are opened fractionally then there willbe a humidified gas stream 210C combining with the dry gas stream 210Dto form the humidified gas flow 210B. Controlling the relative positionsof the upper and lower butterfly valves 1116, 1118 enables the level ofhumidity in the gas flow path 210B to be varied.

The upper and lower butterfly valves 1116, 1118 may be actuated by anysuitable electrical and/or mechanical systems (not shown) available to aperson skilled in the art of miniature motion systems. The actuationmethod may be controlled by a controlling unit (not shown) eitherlocated with the respiratory apparatus or as a separate controllingunit. The controlling unit may in turn be controlled by a humiditysensor or humidity controller.

FIG. 13 is an alternative embodiment to the above butterfly valves,where a sliding shutter 1310 with an aperture 1312 is used to controlthe relative amounts of the humidified and dry gas streams 210C, 210D.The shutter 1310 position shown in FIG. 13 is obstructing the upperpassage layer 1114 at its exit end so that gas flow 210 ispreferentially via the lower passage layer 210C. Thus, the ambient gasflow 210A is humidified by its passage through the lower passage layer210C.

FIG. 14 shows the shutter 1310 when it has been slid partially downwardsin the direction of the arrow. In this position, the aperture 1312partially obstructs the upper passage layer 1114 such that there is apartial dry gas flow stream 210D. Correspondingly, the lower end of theshutter partially obstructs the lower passage layer 1112 so that thereis also a partial humidified gas flow stream 210C. In such a manner, themovement of the sliding shutter can be used to vary the humidity of thehumidified gas flow 210B.

FIG. 15 illustrates the end portion of the sliding shutter 1310 fullyobstructing the lower passage layer 1112 whilst the aperture 1312 allowsthe dry gas stream 210D to flow freely through the upper passage layer1114. In this shutter 1310 position, there is no additionalhumidification of the gas flow 210A.

The actuation of the sliding shutter 1310 may be by any suitableelectrical and/or mechanical systems (not shown) that are readilyavailable to a person skilled in the art of miniature motion systems.The controlling (not shown) of the sliding shutter 1310 position may bein the same manner as described for the butterfly valve embodimentabove.

FIG. 16 shows an alternate embodiment to the use of the butterfly valvesor sliding shutter for humidity control. In FIG. 16, the plate 1110 isattached to a shaft 1610. The central section of the plate 1110, wherethe shaft 1610 is attached, is flexible such that if the shaft is moveddownwards as indicated by the arrow the lower surface of the plate 1110may obstruct the lower passage layer 1112 thereby preventing thehumidified gas flow stream 210C whilst allowing the dry gas stream 210Dto flow. A threaded thumb wheel 1612 may be wound manually to move theshaft 1610 appropriately.

If the shaft 1610 is moved upwards, using the thumb wheel 1612, asindicated by the arrow the upper passage layer 1114 may be obstructedthereby preventing the dry gas stream flow 210D whilst allowing thehumidified gas flow stream 210C. The vertical position of the shaft 1610may thus be used to control the level of humidity of the humidified gasflow 210B.

The actuation of the shaft 1610 may be by any suitable electrical and/ormechanical systems that are readily available to a person skilled in theart of miniature motion systems. The controlling (not shown) of theshaft 1610 vertical position may be in the same manner as described forthe butterfly valve and sliding valve embodiments above.

Overlapping Blade Arrangement

FIG. 17 schematically shows yet another alternative embodiment forhumidity control. The overlapping blade arrangement comprises of avariable aperture 1710 formed by two overlapping blades, a stationaryblade 1712 and a moving blade 1714. The variable aperture controls theamount of interaction between the source of water vapour 216, the firstcompartment wall 212, and the gas flow path 210 in the gas passage layer213. FIG. 17 illustrates the fully open aperture state where the movingblade 1714 is fully retracted into the underside recess 1716 of thestationary blade 1712. In the fully open aperture state, all of thewater vapour 216 which may issue from the first compartment wall 212 isavailable for mixing into the gas flow 210 in the gas passage layer 213.

In the fully closed aperture state, the moving blade 1714 would extendfrom the underside recess 1716 until moving blade 1714 completely coversthe variable aperture 1710. In such a fully closed aperture state, thereis no transfer of water vapour 216 into the gas flow 210 in the gaspassage layer 213, thus no humidification of the gas flow 210 occurs inthe humidifier apparatus 110. In between the fully closed and fully openaperture states any number of humidification rates may be obtained byadjusting the position of the moving blade 1714. In the embodiment ofFIG. 17, three sets of blades 1712, 1714 with corresponding variableapertures 1710 are shown. Each set of blades may be operatedindependently or in a synchronised fashion with the other blade sets.The operation of the blades may be by a mechanical device controlledmanually or an electro-mechanical device with a computer or analoguecircuit servo controller that operates in response to a humidity and/ortemperature sensor or any suitable miniature actuation system availableto a person skilled in the art.

In further alternative embodiments to the above overlapping bladearrangement, a variable level of exposure of the first compartment wall212 to the gas flow 210 in the gas passage layer 213 may be achieved by:

-   -   A retractable full width blade across the first compartment wall        212.    -   Two sets of co-axial and overlapping radial blades adjacent to        the first compartment wall 212. The radial blade arrangement        operates by rotating one or both blade sets in opposite        directions so as to open or reduce the radial apertures formed        between the radial blades.    -   A variable aperture may be formed by use of an iris diaphragm.        Heater Apparatus and Humidity Control

In a further alternate embodiment for the humidity control, the heaterapparatus 220 embodiments as described above may be used with or withoutthe use of the other humidity control embodiments described above.

Water Reservoir

The water supply may comprise a temporary connection of a singlefilling, as described with reference to FIG. 3 above, at the start of anovernight therapy session of CPAP for OSA.

FIG. 18 is a partial, cross-sectional view of a further embodiment ofFIG. 3 where an external water reservoir 1810 rests upon the low profilecentre section 116 of the housing 112. The external water reservoir 1810has a drain 1812 which mates with the water inlet passage 120 so thatwater 1814 may be supplied as a gravity feed to the humidifier apparatus110. The external water reservoir 1810 may have a capacity of 200 to1000 ml or may be any desired volume depending on the application andthe desired humidification capacity of the humidification apparatus.

In an alternative embodiment, the external water reservoir 1810 may belocated elsewhere, such as with other components of the respiratoryapparatus. A micro-pump may then be used to supply the water to thewater inlet passage 120.

FIG. 19 is a different, partial cross-sectional view of the embodimentof FIG. 18. The cross-section taken is as per that for FIG. 2 above.FIG. 19 schematically illustrates a fastening device to secure the waterreservoir 1810 to the housing 112. Two or more flexible latches 1910 areused to engage a rim 1912 of the external water reservoir 1810, e.g.,snap-fit attachment. The flexibility of the latches 1910 is such thatthey may be manually pried apart to disengage from the rim 1912 of thewater reservoir 1810. Refitting the external water reservoir 1810 may bedone by using the snap-clip feature of the latches 1910 as the externalwater reservoir 1810 is pushed onto the housing 112 at the low profilecentre section 116. In an embodiment, the flexible latch may be providedabout the entire perimeter.

Application to Existing Respiratory Apparatus

In a further embodiment, the humidifier apparatus may have adaptationswhich enable it to be accommodated into existing, conventionalrespiratory apparatus in order to improve the performance of therespiratory apparatus. The overall shape of the humidifier apparatus 110may be varied in order for it to attach with an existing respiratoryapparatus. The base plate 222 may be configured appropriately to makethe required thermal and/or electrical contact with the respiratoryapparatus. The gas inlet and outlet 114, 118 may be configured to makean appropriate gas seal with the corresponding gas fixtures of theexisting respiratory apparatus.

Additional Advantages

The humidifier apparatus 220 with the thin gas passage layer 213 upon aplanar water distribution member 211 offers the advantage of having avery high surface area of interaction between the gas flow 210 and thesource of water vapour 216. The comparatively small volume of liquidwater 214 within the water distribution member 211 compared withconventional tub humidifiers gives an additional advantage of ahumidifier apparatus 110 with a very low thermal inertia. Such a systemmay have a rapid thermal response for the production and cessation ofwater vapour 216 for the humidification of the gas flow 210.

The use of an envelope about the water layer 214 by the waterdistribution member 211 reduces the problem of tilting and consequentialspillage of water that a conventional tub humidifier is prone to.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. Also, the various embodiments described abovemay be implemented in conjunction with other embodiments, e.g., aspectsof one embodiment may be combined with aspects of another embodiment torealize yet other embodiments. Further, each independent feature orcomponent of any given assembly may constitute an additional embodiment.Furthermore, each individual component of any given assembly, one ormore portions of an individual component of any given assembly, andvarious combinations of components from one or more embodiments mayinclude one or more ornamental design features. In addition, while theinvention has particular application to patients who suffer from OSA, itis to be appreciated that patients who suffer from other illnesses(e.g., congestive heart failure, diabetes, morbid obesity, stroke,bariatric surgery, etc.) can derive benefit from the above teachings.Moreover, the above teachings have applicability with patients andnon-patients alike in non-medical applications.

What is claimed is:
 1. A water distribution member for a humidifier apparatus, the water distribution member comprising: an envelope formed by a first, substantially planar compartment wall and a second, substantially planar compartment wall joined together along a peripheral edge of the envelope a water inlet opening into the envelope formed in a laterally-offset portion of said first substantially planar compartment wall, said laterally-offset portion extending outwardly of remaining portions of said peripheral edge; and a heater element configured to be disposed below liquid water when in use, wherein the first substantially planar wall comprises at least in part a semi-permeable membrane, the semi-permeable membrane being configured to prevent liquid water from passing through while being structured to allow water vapour to pass through, and wherein the heater element is integrated with the second substantially planar compartment wall and wherein the second substantially planar wall is configured to conduct heat.
 2. The water distribution member according to claim 1, wherein the semi-permeable membrane comprises a finely perforated material.
 3. The water distribution member according to claim 1, wherein the semi-permeable membrane comprises a hydrophobic material.
 4. The water distribution member according to claim 1, wherein the water distribution member is adapted to be a removable and replaceable fitting to the humidifier apparatus.
 5. The water distribution member according to claim 1, further including a water filter in communication with the water inlet.
 6. The water distribution member according to claim 1, wherein the heater element comprises a heater plate.
 7. The water distribution member according to claim 1, wherein the envelope defines a thin water layer having a thickness of less than about 1 mm.
 8. The water distribution member according to claim 1, wherein the envelope defines a thin water layer having a thickness of less than about 5 mm.
 9. The water distribution member according to claim 1, wherein the envelope has a volume of less than about 150 ml.
 10. The water distribution member according to claim 1, wherein the envelope has a volume of less than about 100 ml.
 11. The water distribution member according to claim 1, wherein said second substantially planar compartment wall is comprised of a metal, metal plastic composite or metalized plastic film.
 12. The water distribution member according to claim 1 wherein said first and second substantially planar compartment walls are joined by a bonding strip extending about peripheral edges thereof.
 13. The water distribution member of claim 1 wherein a filter is located within said water inlet.
 14. The water distribution member of claim 13 wherein said filter is supported by one or more ribs.
 15. The water distribution member of claim 13 wherein said filter is comprised of a filter disc supported on an underlying support, and wherein the filter disc coincides with said water inlet in said first substantially planar compartment wall.
 16. The water distribution member of claim 15 wherein said underlying support is provided with one or more ribs.
 17. A water distribution member for a humidifier apparatus comprising an envelope formed by a first, substantially planar compartment wall and a second, substantially planar compartment wall joined together along a peripheral edge of the envelope, and a water inlet opening into the envelope formed in a laterally-offset portion of said first substantially planar compartment wall, said laterally-offset portion extending outwardly of remaining portions of said peripheral edge; wherein the first substantially planar wall comprises at least in part a semi-permeable membrane, the semi-permeable membrane being configured to prevent liquid water while being structured to allow water vapour to pass through, and wherein a heater element is incorporated in the second substantially planar compartment wall.
 18. The water distribution member according to claim 17, wherein the heater element comprises an induction receiving element.
 19. Humidifier apparatus for a respiratory apparatus, comprising: a housing; one or more water supply distribution members removably fitted to the housing, wherein said one or more water supply distribution members comprises an envelope formed by a first upper, substantially planar compartment wall and a second lower, substantially planar compartment wall joined together along a peripheral edge of the envelope, a water inlet opening into the envelope formed in a laterally and outwardly-offset portion of said first substantially planar compartment wall, said laterally and outwardly-offset portion extending outwardly of remaining portions of said peripheral edge, wherein the first substantially planar compartment wall comprises a semi-permeable membrane being configured and arranged to prevent liquid from passing through and being configured to deliver water vapour to one or more gas flow paths defined by the one or more water supply distribution members and the housing; and a heater apparatus in thermal communication with at least one of the water distribution members, the heater apparatus configured to be disposed below liquid water when in use, wherein the heater apparatus is integrated with the second substantially planar compartment wall.
 20. The humidifier apparatus of claim 19 wherein the semi-permeable membrane comprises a hydrophobic material.
 21. The humidifier apparatus of claim 19 wherein the heater apparatus comprises a filament or tape heater.
 22. The humidifier apparatus of claim 19 wherein the heater apparatus comprises an induction heater.
 23. A humidifier apparatus, comprising: a base plate removably and replaceably attachable to a humidifier housing, the housing having a gas inlet, a gas outlet and a first water inlet; a heater apparatus provided to the base plate; and a water distribution member provided to the base plate, the water distribution member including first and second compartment walls joined together along a peripheral edge that define an envelope adapted to receive a supply of water via a second water inlet substantially aligned with said first water inlet, the first water inlet formed in a laterally-offset portion of the first compartment wall, said laterally-offset portion extending outwardly of remaining portions of said peripheral edge, the first compartment wall including a semi-permeable membrane adapted to prevent liquid from passing through and allow water vapour to pass therethrough and the second compartment wall including a thermally conductive wall in thermal communication with the heater apparatus, the heater apparatus configured to be disposed below liquid water when in use, the heater apparatus being integrated with the second compartment wall, and wherein said first water inlet in said housing increases in transverse cross section in an inward direction in order to distribute the water over a filter within the water distribution member.
 24. The humidifier apparatus of claim 23 wherein the housing provides a gas flow path, and wherein a plate is located in said gas flow path, above said water distribution member, and configured and arranged to divide the gas flow path into two gas streams such that only one gas stream receives water vapour from the water distribution member and one or more devices are arranged to control the amount of gas flow into one or both gas streams.
 25. The humidifier apparatus of claim 24 and further including one or more variable apertures placed between the water supply distribution member and the gas flow path.
 26. The humidifier apparatus of claim 25 wherein the one or more variable apertures are structured to regulate the amount of water vapour transferred to the gas flow path.
 27. The humidifier apparatus of claim 23, wherein the semi-permeable membrane is hydrophobic.
 28. A water distribution member for a humidifier apparatus, the water distribution member comprising: an envelope formed by a first, substantially planar compartment wall and a second, substantially planar compartment wall joined together along a peripheral edge of the envelope; a water inlet opening into the envelope formed in a laterally-offset portion of said first substantially planar compartment wall, said laterally-offset portion extending outwardly of remaining portions of said peripheral edge; wherein the second substantially planar compartment wall includes a thermally conductive wall; wherein said second substantially planar compartment wall is comprised of a metal, metal plastic composite or metalized plastic film and configured to prevent both liquid water and water vapour from passing therethrough; and wherein the first substantially planar wall comprises at least in part a semi-permeable membrane, the semi-permeable membrane being configured to prevent liquid water from passing through while being structured to allow water vapour to pass through.
 29. The water distribution member of claim 28, wherein the semi-permeable membrane is hydrophobic. 